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package com.example.performance.jmh.official;

import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * So far all the tests were symmetric: the same code was executed in all the threads.
 * At times, you need the asymmetric test.
 * JMH provides this with the notion of @Group, which can bind several methods together,
 * and all the threads are distributed among the test methods.
 * <p>
 * Each execution group contains of one or more threads.
 * Each thread within a particular execution group executes one of @Group-annotated @Benchmark methods.
 * Multiple execution groups may participate in the run.
 * The total thread count in the run is rounded to the execution group size,
 * which will only allow the full execution groups.
 * <p>
 * Note that two state scopes: Scope.Benchmark and Scope.Thread are not covering all
 * the use cases here -- you either share everything in the state, or share nothing.
 * To break this, we have the middle ground Scope.Group, which marks the state to be
 * shared within the execution group, but not among the execution groups.
 * <p>
 * Putting this all together, the example below means:
 *  a) define the execution group "g",
 *     with 3 threads executing inc(),
 *     and 1 thread executing get(),
 *     4 threads per group in total;
 *  b) if we run this test case with 4 threads, then we will have a single execution group.
 *     Generally, running with 4*N threads will create N execution groups, etc.;
 *  c) each execution group has one @State instance to share:
 *     that is, execution groups share the counter within the group, but not across the groups.
 */
@SuppressWarnings({"java:S101", "java:S100"})
@State(Scope.Group)
@BenchmarkMode(Mode.AverageTime)
@Warmup(iterations = 5, time = 1)
@Measurement(iterations = 5, time = 1)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class JMHSample_15_Asymmetric {

    private AtomicInteger counter;

    @Setup
    public void up() {
        counter = new AtomicInteger();
    }

    @Benchmark
    @Group("g")
    @GroupThreads(3)
    public int inc() {
        return counter.incrementAndGet();
    }

    @Benchmark
    @Group("g")
    @GroupThreads(1)
    public int get() {
        return counter.get();
    }

    /**
     * ============================== HOW TO RUN THIS TEST: ====================================
     * <p>
     * You will have the distinct metrics for inc() and get() from this run.
     * <p>
     * You can run this test:
     * <p>
     * a) Via the command line:
     *    $ mvn clean install
     *    $ java -jar target/benchmarks.jar JMHSample_15 -f 1
     *    (we requested single fork; there are also other options, see -h)
     * <p>
     * b) Via the Java API:
     *    (see the JMH homepage for possible caveats when running from IDE:
     *      <a href="http://openjdk.java.net/projects/code-tools/jmh/">...</a>)
     */
    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(JMHSample_15_Asymmetric.class.getSimpleName())
                .forks(1)
                .build();

        new Runner(opt).run();
    }

}